This invention relates to a motor vehicle suspension system and more particularly to an improved suspension system for a motorcycle.
There has been proposed a type of suspension system for vehicles wherein pairs of shock absorbers are interrelated through a control and interconnecting conduit so as to provide some interaction between the shock absorbers. For example, a system is shown in U.S. Pat. No. 5,486,018, assigned to the assignee hereof, wherein a pair of shock absorbers for a vehicle may be connected either front to rear or side to side so as to provide shock absorbing and also control for either pitch or roll. It has also been proposed to embody such a suspension system in a motorcycle and FIG. 1 illustrates a prior art type of application of this principal.
Referring specifically to this figure, the system includes a front shock absorber 11F and a rear shock absorber 11R. Each of these shock absorbers has a respective piston 12 and 13, which divides the shock absorber into upper chambers 14 and 15 and lower, chambers 16 and 17, respectively. The pistons 12 and 13 reciprocate in cylinders 18 and 19 of the respective shock absorbers 11F and 11R and define these two chambers 14 and 16 and 15 and 17, respectively. The pistons 12 and 13 are connected by respective piston rods 21 and 22 to suitable elements of the vehicle either the vehicle wheel suspension system or the vehicle frame. The cylinders 18 and 19 have trunions 23 and 24 that are connected to the other of the suspension system or vehicle frame.
Flow passages 25 and 26 are provided in the shock absorbers and each has a flow restricting orifice 27 and 28 therein. The size of these orifices determines the damping characteristics.
When the pistons 12 and 13 move upwardly to compress the fluid in the chambers 14 and 15, some of the displaced fluid will flow through the orifices 27 and 28 to the chambers 16 and 17, respectively. However, the positioning of the piston rods 21 and 22 in these chambers occupies some volume and more fluid is displaced from the chambers 14 and 15 than can be accommodated in the chambers 16 and 17.
In accordance with the invention of those earlier mentioned prior art constructions, a conduit having branches 29 and 31 is connected to a damping and control device, indicated generally by the reference numeral 32. This damping and control device 32 is comprised of an outer housing 33 having a pair of chambers 34 and 35 with a dividing wall formed there between. The chamber 34 communicates with a first fluid volume 36 that is formed by an annular portion 37 of a piston 38. A second fluid chamber 39 is formed below this piston 38.
The housing 33 also defines a further fluid chamber 41 that acts on a head portion 42 of the compound piston 38 having the annular portion 37. The areas of the piston head 41 and annular piston portion 37 are equal so that when an equal amount of fluid is displaced from the chambers 14 and 15, the piston 38 will move downwardly so as to accommodate this flow first from the chamber 34 and second from the chamber 35 through a passageway 43 formed internally in the housing 33.
Hence, when the same force is applied and the same displacement of the shock absorber pistons 12 and 13 is experienced, only the damping provided by the orifices 27 and 28 dampens each wheels movement.
If, however, there is a force tending to cause unequal displacement, then flow occurs through an orifice passageway 44 connecting the chambers 34 and 35 so as to provide further damping. If the shock absorbers 11 are mounted on the front or rear wheels, then the damping will control roll. If, on the other hand, the shock absorbers 11 are disposed at front and rear wheels, then pitch and squat are dampened. When used in a motorcycle having only a single front and single rear wheel, this provides dive and squat control.
However, this type of system is effective primarily when the shock absorbers 11 associated with each wheel have the same construction and each bears the same load. However in a motorcycle, the rear shock absorber is more heavily loaded and hence, is usually larger and less compliant than the front shock absorber. As a result, the application of the prior art construction shown in FIG. 1 gives an undesirable effect when applied in a motorcycle.
For example, when both the front and rear wheels experience the same load, then an additional damping is effected by the passage through the orifice 44 which may be undesirable. In addition, this can provide a bouncing motion to the vehicle.
Also, when there is rapid deceleration or rapid acceleration, the dive and squat characteristics will be different and this presents an undesirable effect.
In my aforenoted, copending application there is disclosed an arrangement for primarily a four wheel vehicle where paired shock absorbers have different constructions. Although that application makes reference to the possible use of that construction on vehicles having less than four wheels, such an embodiment is not specifically described nor illustrated.
Therefore, it is a principal object to this invention to provide a suspension system of this type which is particularly adapted for use in motorcycles wherein the two interconnected shock absorbers are constructed differently so as to provide different damping characteristics.
It is a further object to this invention to provide an improved suspension for motorcycles.
It is a yet further object to this invention to provide an interconnected hydraulic damping suspension system for motorcycles wherein the utilization of different shock absorbers for the front and rear wheels can be employed with adverse affects due to the interconnection between the shock absorbers.
This invention is adapted to be embodied in a suspension system for a motorcycle having two wheels spaced along the length of the vehicle body frame. Suspension systems mount each of the wheels for suspension movement relative to the vehicle body frame. A front damping element had a pair of relatively moveable members that define a first fluid chamber and is interposed between the forward most of the wheels and the vehicle body frame for varying the volume of the first fluid chamber upon suspension of the forward most wheel. A first damping arrangement is provided for damping the flow from the first chamber. A rear damping element also having a pair of relatively moveable members defines a second fluid chamber. The rear damping member is interposed between the other of the wheels and the vehicle body frame for varying the volume of the second fluid chamber upon suspension movement of the other wheel. A second damping arrangement dampens the flow of fluid from the second fluid chamber. The first and second damping elements each have different constructions so that the application of a given force to each of them will affect a different flow from the respective fluid chamber thereof. A conduit interconnects the first and second fluid chambers. A control arrangement in the conduit precludes fluid flow through the conduit in response to a first suspension condition and provides a damped flow through the conduit in response to a second suspension condition.